Unit 3 Part 1Atomic Structure

ICPMr. Patel

SWHS

Topic OutlineLearn Major ElementsThe Atom Subatomic Particles Modern Atomic Theory Organizing the ElementsPeriodic TableClassifying ElementsAtomic Models

Defining the AtomAtom – the smallest particle of an

element that retains its identityCan not see with naked eyeNanoscale (10-9 m)Seen with scanning

tunneling electronmicroscope

DemocritusDemocritus was a Greek to first

come up with idea of an atom.

His belief: atoms were indivisible and indestructible. = WRONG!

Atom comes from “atmos” - indivisible

Dalton’s Atomic Theory2000 yrs later, John Dalton used

scientific method to transform Democritus’s idea into a scientific theory

Dalton put his conclusions together into his Atomic Theory (4 parts)

Dalton’s Atomic Theory1. All elements are composed of

indivisible atoms.

Dalton’s Atomic Theory2. Atoms of the same element are

identical. Atoms of different elements are different

Dalton’s Atomic Theory3. Atoms of different elements can

chemically combine in whole number ratios.

Dalton’s Atomic Theory4. Atoms of one element can never be

changed to another element

The ElectronParticle with negative charge

Discovered by J.J. Thomson

Used cathode ray (electron) beam and a magnet/charged plate.

Millikan found the charge and mass

The Proton and NeutronAn atom is electrically neutral

If there is a negative particle then there must be positive particle

Proton – particle with positive charge

Chadwick discovered neutron – neutral charge

Thomson’s Atomic ModelElectrons distributed in a sea of

positive chargePlum Pudding Model

Rutherford’s Gold Foil Experiment

Rutherford’s Atomic ModelThe nucleus is the central part of the

atom containing protons and neutronsPositive chargeMost of the mass

Electrons are located outside the nucleusNegative chargeMost of the volume

Atomic Number An element is defined only by the

number of protons it contains

Atomic Number – number of protons

Number of protons = number of electronFor a neutral element

Identify the number of Protons1. Zinc (Zn)

2. Iron (Fe)

3. Carbon (C)

4. Uranium (U)

1. 30

2. 26

3. 6

4. 92

Mass NumberNucleus contains most of the mass

Mass Number – total protons and neutrons

Number of neutron = Mass # – Atomic #

Identify # of Subatomic Particles1. Lithium

(MN = 7)

2. Nitrogen(MN = 14)

3. Fluorine(MN = 19)

**MN = Mass Number

1. 3 p+ , 3 e-, 4 n0

2. 7 p+ , 7 e-, 7 n0

3. 9 p+ , 9 e-, 10 n0

Differences in Particle NumberDifferent element: different number of

protons

Ions – same number of proton, different number of electrons

Isotope – same number of proton, different number of neutronsDifferent Mass Numbers

Two Notations for AtomsNuclear Notation

Write the element symbolOn left side, superscript = Mass NumberOn left side, subscript = Atomic Number

Isotope –Hyphen NotationWrite full name of elementOn right side, put a dashOn right side put Mass Number after dash

Hydrogen - 3

Ex: Three isotopes of oxygen are oxygen-16, oxygen-17, and oxygen-18. Write the

nuclear symbol for each.

Ex: Three isotopes of chromium are chromium-50, chromium-52, and chromium-53. How many neutrons are in each isotope?

Ex: Calculate the number of neutrons for 99

42Mo.

Atomic MassAtomic Mass Unit (amu) – one-twelfth of

the mass of the carbon-12 atom

Different isotopes have different amu (mass) and abundance (percentage of total)

Atomic Mass – weighted average mass of the naturally occurring atoms.Isotope MassIsotope Abundance

Atomic MassBecause abundance is considered, the

most abundant isotope is typically the one with a mass number closest to the atomic mass.

Example, Boron occurs as Boron-10 and Boron-11. Periodic Table tells us Born has atomic mass of 10.81 amu.Boron-11 must be more

abundant